1. Technical Field of the Invention
The present invention relates to telecommunications systems and, in particular, to implementing a call trace mechanism at the network level in a telecommunications system.
2. Description of Related Art and Objects of the Invention
Today's telephone networks provide many new, exciting, and convenient features. For example, caller identification (ID), call blocking, and call return were not available a few years ago, but they are greatly appreciated by many people today. The telephone network of today that enables these features is actually composed of two networks. The first network provides control and signaling capabilities, while the second network transmits the actual voice and data information of the telephone user.
The control and signaling network is commonly termed Signaling System #7 (SS7). It began as a means to enable toll-free 800 numbers and evolved to provide much more, such as caller ID as noted above. As an additional example of what SS7 provides: SS7 is used to remotely control the voice and data network (voice network). The voice network itself is composed of, in part, switches, user telephones, interconnecting voice trunks, and linking phone lines.
Referring now to FIG. 1, SS7/voice network 100 is diagramed. Though the SS7 network is separate from the voice network, they are diagramed together for two reasons. First, diagraming them together facilitates an understanding of the logical interrelationship between the two networks. Second, the computers that comprise the SS7 network are often physically located within the same exchange offices as the telephone switches.
Continuing with FIG. 1, the signaling paths of the SS7 network are denoted by the solid lines 110 while the voice trunks are denoted by the broken lines 120. The multiple SSP/Switches 130 represent two elements. The Service Switching Point (SSP) is the local exchange in the telephone network. It should be understood that the term "SSP" can actually connote (i) a combination voice switch and SS7 switch or (ii) an adjunct computer connected to the local exchange's voice switch. In other words, "SSP" represents both the SS7 and the voice network and will be so used except in connection with FIG. 1, where "SSP/Switch" is used to highlight the distinction between the two networks. Each SSP/Switch 130 is connected to at least one other SSP/Switch 130 by a voice trunk 120, which provides the conduit for the voice and data traffic of the user.
Each SSP/Switch 130 is also connected to the remainder of the SS7 network via signaling paths 110 to at least one Signal Transfer Point (STP) 140. The multiple STPs 140 route the messages that are transmitted over the SS7 network to control operation of the voice network. It is noted that some SSP/Switches 130 are directly connected to other SSP/Switches 130 via a direct SS7 signaling path 170. Continuing with the operation of the SS7 network, select STPs 140 are in communication with a Service Control Point (SCP) 150. The SCPs 150 are interfaces to telephone company databases, which store information about subscribers' services, routing of special service numbers (e.g;, 800 and 900 numbers), calling card validation, Advanced Intelligent Network (AIN) services, etc. Finally, Operations Support Services (OSSes) 160 represent the remote maintenance centers for the monitoring and management of the SS7 network.
Message transmission over the signaling paths 110 (and impliedly, the direct SS7 signaling paths 170) is effectuated by using Integrated Services Digital Network (ISDN) User Part (ISUP) signaling. The ISUP protocol enables today's modern telephone features, e.g., call waiting and call forwarding. Moreover, ISUP is the means for establishing a telephone connection from a calling party (originating subscriber), through one or more SSP/Switches 130, and finally to a called party (terminating subscriber). ISUP messages are sent from an originating subscriber's SSP/Switch 130 over the SS7 network, usually through at least one STP 140, to a different SSP/Switch 130. Often the ISUP message for establishing a call passes through multiple SSP/Switches 130; once the terminating subscriber's SSP/Switch 130 is reached via the SS7 network, a voice circuit along voice trunk 120 and through multiple SSP/Switches 130 is also established.
Unfortunately, this setup procedure can be inefficient. The voice circuit will not necessarily be routed along the shortest possible length of the voice trunk 120. This can result in delays for the call setup process and a squandering of parts of the expensive telephone infrastructure, namely voice trunk 120 resources and any extraneous SSP/Switches 130. To avoid wasting the telephone infrastructure, a tool to enhance the ability to test and optimize call routing is needed. A tool that can trace a current routing and submit the trace results for diagnosis is also needed.
The probability of inefficient routing is exacerbated with another new feature of today's telephone network: local number portability (LNP). With reference now to FIG. 2 for an example of an LNP 200. Traditionally, each SSP 235, 245, and 250 is assigned a set of phone numbers, typically based on the first three of the seven phone digits. (It is reiterated here that "SSP" actually connotes both an interface to the SS7 network and a switch in the voice network and that it will be used in this context throughout the remainder of the document.) In other words, the SSPs 235, 245, and 250 of the LNP 200 are assigned at least phone numbers 235-XXXX, 245-XXXX, and 250-XXXX, respectively.
Continuing with FIG. 2, the SSPs are connected to one another (directly or indirectly) over the voice network via a voice trunk 240. The SSP 250 is connected to Originating Phone 205 by a linking phone line 230, (delineated by the line/circle combination, and the SSP 235 is also connected to a Terminating Phone 225 by another linking phone line 230'. Each SSP is also connected to the STP 210 along signaling paths 216, which transmit ISUP messages. Finally, the STP 210 is also in communication with SCP 220 along a signaling path 215.
With further reference to FIG. 2, the SSP 250 is an Originating Switch, where the phone call originates; the SSP 245 is an Intermediate Switch, where the phone call must be routed through; and the SSP 235 is a Recipient Switch (the recipient of the ported number), where the phone call to the ported number will ultimately terminate. Another SSP (not pictured) is the Donor Switch, where the ported number was originally assigned. In the LNP 200, a ported number is 255-XXX1. A user at the Originating Phone 205 dials 255-XXX1, and the Originating Switch/SSP 250 utilizes ISUP messages across signaling path 216 to communicate with the STP 210, which (also utilizing ISUP protocol) accesses the databases represented by the SCP 220 to determine which switch is now associated with the ported number 255-XXX1. This information is then forwarded to the Originating Switch/SSP 250, which then begins the call setup procedure. The setup proceeds through the Intermediate Switch/SSP 245 and subsequently terminates on the Recipient Switch/SSP 235.
Unfortunately, most routing does not proceed so simply and efficiently. Several, and even many, intermediate switches may be traversed along the path to a given Recipient Switch. As stated above, inefficient routing already afflicts the telephone system. Additionally, looping and errors in the AIN database also already adversely impact telephone system performance. Now, with the complexity of LNP deployment, there are more opportunities for routing errors at the network level. For instance, some SSPs do not have the ability to recognize a ported number. As a result, the call is initially routed to the donor switch, and then the donor switch consults an SCP to determine the identity of the recipient switch. Finally, the donor switch is able to begin establishing the connection appropriately. This convoluted process further entangles the routing process.
Moreover, at present there are several types of LNP. The LNP 200 described with respect to FIG. 2, for example, is Location Portability, where a phone number is retained after the subscriber physically moves. A second type of LNP is Service Portability, where a phone number is retained after changing services. A third type of LNP is Service Provider Portability, where a phone number is retained after changing phone service providers. These second and third LNP categories also further complicate the routing process and thereby introduce even more opportunities for inefficient or incorrect call routing. Consequently, a tool is needed to enable the detection of exchange routing errors in the network by producing a list of the switches through which a call is routed. Heretofore, there has been no call trace mechanism at the network level using ISUP signaling.
A non-exhaustive list of objects of the invention follows:
An object of the invention is to provide a network call trace ability.
A further object of the invention is to provide a network call trace ability using ISUP signaling.
Another object of the invention is to provide a network call trace ability using ISUP signaling in a SS7 network.
It is also an object of the invention to implement a network call trace by tagging Switch IDs (SIDs) onto the Initial Address Message (IAM).
Yet another object of the invention is to implement a network call trace by using the IAM Generic Digits Parameter (GDP) with a Type of Digit (TOD) Network Call Trace.
A still further object of the invention is to implement a network call trace that returns a list of SIDs to the originating switch in the first backward message.